Apprentice to flat rate advice

Im working in a Ford dealership as a helper for the engine tech. I've been doing this for over two years now. I was offered a position at another Ford dealer as a flat rate technician working on engines.

Im trying to decide, do I accept it or no? The pay is literally double what im at now. I'll be making $40 per flag hour. My only issue is, will i struggle? They're offering to guarantee 40 hours for the first 60 days. If i can't handle it, i won't be able to support my family.

Does anyone have any experience like this? Any advice for someone in my position?